1. Field of Invention
This invention relates to digital circuits. Specifically, the present invention relates to programmable digital filters for use in telecommunications systems.
2. Description of the Related Art
Digital filters are used in a variety of demanding applications ranging from electronic control systems to cellular telecommunications systems. Such applications often require programmable digital filters that consume minimal power.
Digital filter programmability and low power consumption are particularly important in digital cellular telecommunications systems such as code division multiple access (CDMA) systems. A typical CDMA cellular telecommunications system is characterized by a plurality of mobile transceivers in communication with one or more base stations. Signals transmitted by the mobile transceivers are received by a base station and often relayed to a mobile switching center (MSC). The MSC in turn routes the signal to another base station, a public switched telephone network (PSTN) or to another mobile transceiver. Similarly, the public switched telephone network may transmit a signal to a mobile unit via a base station and a mobile switching center.
It is often advantageous to employ different sampling rates within the mobile transceiver, base station, and/or MSC. To accommodate different sampling rates, digital filters located within the mobile transceiver, base station, and/or MSC are often programmable. Filter programmability also reduces the need to replace expensive hardware when mobile transceiver specifications change.
In a typical programmable digital filter, several registers or delay circuits are connected in series. The outputs of the registers are connected to parallel programmable gain circuits having gains related to filter transfer function coefficients. The outputs of the gain circuits are input to multipliers connected in series. The filter design often requires many expensive digital multipliers that consume excess power and occupy valuable circuit board space. The digital multipliers result in large filter power consumption and decreased mobile transceiver battery life.
Hence a need exists in the art for a space-efficient low-power programmable digital filter that can accommodate a range of input frequencies or sample rates. There is a further need for a power-efficient transceiver incorporating a low-power programmable digital filter.